I'm trying to use my LM317t to take the arduino 5v to 1.5v, which is the voltage I need for my transformer to power my nixie tubes. I can use my nixie tubes off a AA battery from the transformer just fine. And I can get 1.5v out of my LM317t just fine. But when I try to connect the 1.5v into the transformer, my arduino voltage drops to 3 to 4v. This makes my 74141 not work, and I would imagine isnt good for the arduino/atmega. Can anyone help me out, what's going on here?

Hi, Are you running all this from the USB?? Better to get a 9V to 12V external plug-in supply, and

Suggestion:1. Plug it into Arduino External power jack. Power the Arduino that way.2. ALSO feed the LM317 from the 9 Volts. It will still put out 1.5 V (Or whatever voltage you have set with the resistor ratio; I assume you have that figured out)..

Hmm, it's still not working, even with a 750ma power supply. The only way to get it to work is to give the 74141 its own separate 5v source. The LM317t is draining it's 5v down to 3-4v still, whether It's in parallel with the 5v regulator or pulling from the 5v regulator. I'm only using one nixie tube, could it require more than 750ma?

looking at the spec sheets the 74141 runs 25ma, the LM317 and put out 1.5A so figure 2A in at full load.Also looking at the info on that page I think you need to look at the hookup schematic. http://www.national.com/mpf/LM/LM317.html#Overview

Yes, thats what i meant by in parallel with the 5v regulator. I have them both running straight off the power supply and I get similar results.

The thing is though, the nixie tube works fine off the 750ma power supply, as long as i get the 5v somewhere else. So i found a 1.6A power supply, and I still have the same problem, even though more than twice as much amperage is available. I thought this was weird because obviously the nixie tube is getting enough power from 750ma, which leaves more than 750ma more available for everything else. Is this an incorrect assumption?

Tt lights fine when i manually wire the nixie. The 5v stays 5v, the 1.5 drops a little but the transformer still lights the nixie fine. Its only when i have it wired to the 74141 that I get this problem.

Maybe high-frequency noise / coupling?? Make sure you have a bypass capacitor (say .1uf) right across the 74141 Vcc-Gnd supply. Make sure you have a similar value (but you may need a 200v or more rating) across the DC output of your Nixie power supply...

I can use my nixie tubes off a AA battery from the transformer just fine.

I'm a little confused. You are talking about nixie tubes, batteries and transformers all in the same sentence. Unless there are some modern replacements the nixie tubes that I remember were neon devices that required high voltage to operate. Also, the batteries that I am familiar with produce DC (as does the LM317) and transformers transform AC (or sometimes chopped up DC).

Im using this tutorial: http://www.instructables.com/id/Disposibal-Camera-Nixie-Tube-Driver/The battery goes in to the flash transformer, and comes out 200 or so volts.

Anyway the de-coupling capacitors didn't make a difference. But since I've taken it apart, and re-wired it now it's the 1.5 that drops, so my 5v is fine but the transformer is only outputting a few volts. It's just something about the Vcc pin of the 74141 being connected to the rest of my setup that causes problems. Everything is fine when the 5v comes from the arduino board, and from my power supply I get 5v powering an LED just fine and the 1.5 from the LM317t powering the transformer and my Nixies just fine. I've got the thing ticking 0-9. But when that 5v pin goes from the arduino board to my 5v line on the breadboard the 1.5v dies.

Ugh. I'm thinking about making a 555 nixie power supply (http://www.ledsales.com.au/kits/nixie_supply.pdf) but the way this is acting, im afraid after I go to all the work, it wont make a difference.

I really appreciate the help so far, guys. If you have any more suggestions it would be really helpful. Thanks.